Using the definition of Gamma function [1]}, we can express \(E_k\)  as
\({E_k} = \frac{{{\color {black}{\lambda } _1}^{{\color {black}{\lambda } _2}}}}{{2\Gamma \!\left( {{\color {black}{\lambda } _2}} \right)}}\int _0^\infty {{x^{{\color {black}{\lambda } _2} - 1}}{e^{ - {\color {black}{\lambda } _1}x}}{F_{{\gamma _k}}}\left( x \right){\rm {d}}x}.\) 
